1. Field of the Invention
The present invention relates to a full-circumferential flow pump, and more particularly to a full-circumferential flow pump which has an impeller mounted on an end of the shaft of a motor and an annular space defined around the motor.
2. Description of the Prior Art
One known pump in which the fluid being handled flows circumferentially around the motor is disclosed in German laid-open patent publication No. 1653692 (DE 1653692). The disclosed pump allows the shaft to be rotated manually and the pump assembly to be serviced without the piping's being detached.
FIG. 18 of the accompanying drawings shows such a known pump. As shown in FIG. 18, the pump has a block-shaped housing 100 which houses a motor comprising a stator 101 and a rotor 102 that is positioned within the stator 101 with a small gap defined therebetween. Impellers 103, 104 are mounted on the respective ends of the shaft of the rotor 102. The fluid which is being handled flows in from an inlet port 105 and is divided into two fluid flows which are pressurized by the respective impellers 103, 104 which are being rotated. The fluid forced out of the impellers 103, 104 merges and is then discharged from an outlet port 106.
In the known pump, however, the stator 101 is subject to pressure irregularities and tends to suffer various mechanical failures. Specifically, there are developed three regions on the outer circumferential surface of the motor. These three regions include:
(1) a region where the fluid flows under the inlet suction pressure; PA1 (2) a region where the fluid flows under the outlet discharge pressure; and PA1 (3) a region where the fluid does not flow. Accordingly, pressures or external forces which are not uniform are applied to the stator 101, possibly causing the stator 101 to be strained or deformed.
The motor is highly likely to undergo mechanical distortions particularly if an outer motor frame casing is made of thin sheet metal or the pressure for discharging the fluid is high. Furthermore, since the outer motor frame casing and an outer pump casing are integrally formed with each other in the disclosed pump, the motor may possibly malfunction when subjected to external forces due to a piping load or the like.